1. Field of the Invention
This invention relates to a video signal processing device and more particularly to a device for processing a video signal including line sequential color difference signals which are provided with characteristic parts for identification of the kinds of information carried by these signals.
2. Description of the Related Art
In detecting the presence or absence of color information within a video signal for the purpose of controlling a so-called color killer circuit, it has been practiced in general, to attain that purpose by detecting the carrier wave components of color information signals and by detecting the levels of them. In the case of a video tape recorder or a television receiver or the like, for example, the levels of the subcarriers in the burst signal parts of chrominance signals have been arranged to be detected. Further, in cases where color information is transmitted by means of line sequential color difference signals which are modulated by an FM modulation process or the like before transmission, the levels of the FM carrier signals have been arranged to be detected for this purpose.
The conventional method for detecting the presence or absence of color information necessitates detection of extremely slight variations in the FM carrier signal in detecting the FM carrier signal. Besides, the level variations are not only caused by the validity of the color information but also greatly attributable to other factors, for example: In the case of an apparatus for reproducing a video signal recorded on a recording medium, the level of the FM carrier signal greatly varies due due to trailing, head touch, etc., even when the color information is accurate. Therefore, in setting a threshold value for the detection circuit, the value must be very delicately adjusted. It is thus hardly possible to accurately detect the presence or absence of color information. As a result, the apparatus of this kind has often produced meaningless color information to degrade a reproduced picture or failed to produce necessary color information. Further, the color information is sometimes produced for an extremely short period of time. In accordance with the conventional method, it has been thus hardly possible to obtain satisfactorily reproduced pictures even when the color information is valid.